msm: defconfig: Enable mixer1 writeback for HDMI

Mdp mixer1 drives HDMI. If HDMI downscaling, e.g. 1080p to 480p,
requires mdp clk more than its max, this feature is enabled to avoid
underrun.

Change-Id: Icfabd54fad002b7582062bbd76c0f3acd01df31d
Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
diff --git a/arch/arm/configs/msm8960_defconfig b/arch/arm/configs/msm8960_defconfig
index 0bb87fb..469cfcf 100644
--- a/arch/arm/configs/msm8960_defconfig
+++ b/arch/arm/configs/msm8960_defconfig
@@ -328,6 +328,7 @@
 CONFIG_FB_MSM_MDP40=y
 CONFIG_FB_MSM_OVERLAY=y
 CONFIG_FB_MSM_OVERLAY0_WRITEBACK=y
+CONFIG_FB_MSM_OVERLAY1_WRITEBACK=y
 CONFIG_FB_MSM_WRITEBACK_MSM_PANEL=y
 CONFIG_FB_MSM_MIPI_PANEL_DETECT=y
 CONFIG_FB_MSM_HDMI_MSM_PANEL=y